(a) Field of the Invention
The present invention relates to a graphene sheet, a transparent electrode and an active layer including the same, a display device, and an electronic device, and an optoelectronic device, a battery, a solar cell, and a dye-sensitized solar cell including the same.
(b) Description of the Related Art
In general, various devices such as a display, a light emitting diode, a solar cell, and the like transmit light to display an image or to produce electric power, and thus necessarily require a transparent electrode transmitting light. The transparent electrode may most widely include indium tin oxide (ITO).
However, as more indium is consumed, the cost of indium tin oxide increases as it becomes scarcer. Further, as a transparent electrode using indium is known to have chemical and electrical characteristic defects, development of an alternative electrode material that can replace the indium is being actively undertaken.
On the other hand, silicon is used for an active layer for an electronic device and a semiconductor device. As an example, a thin film transistor is illustrated here.
In general, a thin film transistor has multi-layers, and in particular, includes a semiconductor layer, an insulation layer, a protection layer, an electrode layer, and the like. Each layer included in the thin film transistor is formed in a sputtering method or a chemical vapor deposition (CVD) method, and is then appropriately patterned through lithography. A thin film transistor is widely used at present, and includes an amorphous silicon layer as a semiconductor layer. The amorphous silicon layer works as a conductive channel in which electrons flow. However, a thin film transistor has a limit in a display due to low electron mobility.
Silicon has carrier mobility of about 1000 cm2/Vs at room temperature.
In order to solve this problem, Japan Patent Laid-Open Publication No. Pyeung No. 11-340473 discloses a thin film transistor prepared by sequentially coating a protection layer and an amorphous silicon layer on a substrate and crystallizing the coated product with a laser to change a polysilicon layer into an active layer. In this method, the protection layer and the amorphous silicon layer are coated in a radio frequency (RF) sputtering method. However, since the RF sputtering method has a problem of uneven thickness as well as a very slow coating speed, and thus forms a layer that is sensitive to laser energy density change, it may form a polysilicon layer with unstable electrical characteristics when the polysilicon layer is crystallized with a laser.
On the other hand, a chemical vapor deposition (CVD) method as opposed to the sputtering method may be used to form a protection layer and a polysilicon active layer. However, this method requires a process temperature of 500° C., and accordingly, a glass substrate may be annealed at the high temperature. In addition, the chemical vapor deposition (CVD) method additionally requires an annealing process to remove hydrogen diffused inside a thin film and causing a critical problem, and accordingly may not form a polysilicon layer with uniform electrical characteristics.
Therefore, a new material needs to be developed to fabricate a faster and better device.